The continually increasing combustion of fossil fuel, such as coal, natural gas, and oil, has resulted in a dramatic increase in the concentration of CO2 in the atmosphere. There is overwhelming evidence that the greenhouse effect is at least partly caused by this increased CO2 concentration and that this has already contributed to the climate changes that have occurred over the last decades. According to simulation models, it is suspected to cause further and potentially more dramatic changes in the climate in the future.
As a result, scientists, environmentalists and politicians throughout the world are driving initiatives to reduce the amount of CO2 discharged into the atmosphere by combustion of fossil fuel. One approach being adopted is to capture CO2 (i.e. prevent the release of CO2) from the exhaust gases, e.g. from thermal power plants, before they are released to the atmosphere. The captured CO2 may be injected into subterranean formations such as aquifers, oil wells for enhanced oil recovery or in depleted oil and gas wells for deposition since tests indicate that CO2 remains in the subterranean formation for thousands of years and is not released back into the atmosphere.
The most common CO2 capture processes are based on the CO2-containing gas mixture being introduced, in counter flow, to an aqueous absorbent in an absorber column. The gas leaving the absorber column is CO2 depleted. The CO2 leaves the absorber column together with the absorbent. Typically the absorbent is subsequently regenerated in a regenerator column and returned to the absorber column. The CO2 separated from the absorbent is sent for storage, e.g. in a subterranean formation.
Several types of aqueous absorbents are utilised in carbon capture processes including amines, carbonates and amino acid salts.
The currently preferred absorbents for use in these processes are, however, aqueous solutions of different amines. The amines used for the CO2 capture, and also the fluids used for emission control and flue gas treatment, however, interact with several of the materials most commonly used in the construction of equipment that is used in the CO2 capture process. For instance the amines may cause corrosion or degradation of the equipment material, particularly the columns, its inserts and piping where the amines are present in significant amounts and at relatively high temperatures.
Polyolefin materials, e.g. polypropylene and polyethylene, are generally very resistant against amines at low and moderate temperatures, and may be used in contact with amines either alone or as liners on less resistant substrates of e.g. steel, concrete, or composite materials. For application in CO2 capture plants, the required service lifetime of a liner is more than 30 years at temperatures up to 80° C. and in amine solution (e.g. 30% monoethanolamine (MEA) in water or similar concentrations of other amines or mixtures of amines).
EP 0657684 A (KERAMCHEMIE GMBH) 14 Jun. 1995 describes construction part for chemical plants where a liner is provided at metal surfaces as corrosion coating, where the liner has a layered structure comprising an inner resin layer fastened to a supporting metal body, and where the inner layer is protected by one or more outer layers, of which the outer layer is a non-diffusive rubber layer.
DE 2105859 A (FRACTIONATION RESEARCH LTD) 7 Oct. 1971 relates to building elements for chemical process plants made of high temperature polypropylene without any metal organic compounds at least in the surface layer. Said building elements are said to be resistant to water and many chemicals.
DE 3820434 A (LINDE AG) 21 Dec. 1989 relates to an absorption column having a packing comprising packing elements made of polymers such as polypropylene or polyethylene. Nothing is said about the nature of the polymers, or their use as a liner.
DE 102009013757 A (LINDE AG) 29 Sep. 2010 describes an absorption column for CO2 capture including a packing of synthetic material, such as plastic. Nothing is discovered about the nature of the synthetic material.
US 2006/0156923 A (BASF AG) 20 Jul. 2006 discloses the idea of using a polypropylene liner in an inert scrubbing column for deacidifying acid gases. Additionally, MOSER, Peter, et al. Material Testing for Future Commercial Post-Combustion Capture Plants. Energy Procedia. September 2011, vol.4, p.1317-1322. tests the performance of a concrete module lined with polypropylene in a flow line returning absorbent to an absorption column. No details about the nature of the polypropylene are, however, revealed in either publication.
MÜLLER, Werner W., et al. Antioxidant depletion and oit values of high impact PP strands. Chinese Journal of Polymer Science. 2009, vol. 27, no. 3, p. 435-445. relates to a study of depletion of different antioxidants in polypropylene (PP) during immersion in water, and inversion of water combined with air oven aging. There is, however, no mentioning of the effects of aqueous solutions as such, or more specifically aqueous amine solutions used as CO2 absorbents on the antioxidants, or on the PP including the antioxidants.
The requirements for the lifetime, or service life, of the construction elements in contact with aqueous amine solutions in a plant for CO2 capture, such as columns, tanks, piping, packing etc, is 30 years. Depletion of antioxidants used to stabilize polyolefins under exposure for the operating conditions the building element comprising a polyolefin will be exposed to, is an indication on the lifetime for the polyolefin. Testing under temperatures higher than the expected operating temperature until degradation or mechanical breakdown of the polyolefin material, is an accepted accelerated test, that can give a better indication on the lifetime.
The tests described by Müller et al, see table 3, indicates that antioxidants as Irganox 1010 and Irganox 1330 are depleted within 120 days in water bath at 90° C., and 301 days at 90° C. Even though it is indicated that for the antioxidant Irganox 1330, OIT values during aging changed slower than the reduction of antioxidant concentration in the polymer, the lifetime for a polyolefin stabilized with Irganox 1330 assumed from the data provided by Müller et al, is far shorter than 30 years. The skilled person reading Müller et al would conclude that other antioxidants different from Irganox 1330 had to be used to provide the required lifetime.
Candidate material, beta (b)-PP BE60-7032 from Borealis AS and, sold by Steuler, as a corrosion resistant polymer, was subjected to long term testing under conditions representative for the conditions in a CO2 absorption column. It was found not to have the required long term resistance to the absorbent. This testing is shown in the examples section.
Hence, there is a need to develop more resistant materials for long term operation for constructing equipment for use in CO2 capture plants. Further goals for the present invention will be apparent for the skilled person in reading the description.